Stopping the forward or rear movement of any land vehicle requires cessation of the rotation of the vehicle wheels. Early solutions utilized a strap encompassing a braking hub on the inner side of the wheel. The strap was in a mounting surrounding this hub and pressing a lever brought the strap into contact with the hub. At this stage of the development of motor powered vehicles, vehicle speeds were low, the wheels were large and composed of a plurality of spokes extending from a central hub to a circumferential ring. To deflect dirt, mud and water from spraying the vehicle outer surfaces, fenders were installed, generally covering only the width of the wheel with its tire. Engine compartments were relatively small and vehicle bodies were well spaced from the wheels. As a result there was always an unobstructed flow of air on both sides of a vehicle's wheels. While this was an advantage in dry weather, the presence of rain could be a disadvantage. The braking strap could become wetted as could the inner surface of the braking hub.
To overcome this problem, a new braking system was developed. Basically, it was the reversed position of the earlier braking system and comprised a pair of opposing arcuate braking segments having friction material on their outer surfaces mounted on a plate fixed to the axle housings of the vehicles and being mounted for outward radial movement in contrast to the constricting movement of the earlier braking band. The braking hub was increased in diameter to encompass the braking segments and thereby substantially reduce the contact by rain with the arcuate segments and the interior of the braking hub. The increased diameter of the braking hub reduced the length of the spokes in a wheel. Initially these spokes were of wood with attendant size for strength. Whether for aesthetic reasons or an unrecognized reasoning, the wooden spokes were replaced by an increased plurality of thin metal spokes. The wire spokes provided more openings around the outer surface of the braking drums. For aesthetic reasons and with more consideration of aerodynamics vehicle bodies began to shroud the wheel openings. The development of disc braking systems resulted primarily in reducing the width of the brake drums but not the diameters.
This development of the braking system does not indicate any consideration in the development design of the temperature increase in the braking drum. The only evident acknowledgement of this potential can be found in the tests made on braking efficiency. These tests are generally reported as "cold braking distances" and "hot braking distances". In all tests the "hot braking distance" is greater than the "cold braking distance".
The current design of vehicle wheels is a large metal central portion covering the interior of the wheel, the braking hub and the four or five circular openings between this central portion and the wheel rim, the openings being primarily to reduce weight. Wheel covers are increasingly becoming discs with only peripheral openings. The result is that the heat generated in tires and wheels during prolonged periods of movement of the vehicle is increasingly trapped within the wheel cover thus contributing to the difference in braking distances between "cold braking" and "hot braking".
Prior to the present invention there is no known attempt to decrease this distance between "cold braking" and "hot braking" by redesigned wheel covers.